This application relates to a method for potting bundles of microporous tubing which may be utilized in diffusion operations such as the oxygenation of blood, membrane plasmapheresis, and the like.
Bundles of capillary tubing are currently in extensive commercial use in dialyzers for blood, with the capillary tubing being typically made of a cellulose-derivative material. These bundles are commercially assembled, and then centrifugally potted in known manner, for example by the technique of U.S. Pat. No. 4,227,295, Method of Potting the Ends of a Bundle of Hollow Fibers Positioned in a Casing, to Bodnar, et al., to enclose the bundle into a tubular housing, with the ends of the bundle of capillary fibers being each sealed in a typically polyurethane potting compound, with the bores of the capillary fibers communicating through the sealant at each end.
A manifold is placed on each end so that the blood is directed through a flow path which passes through the bores of the fibers. Side manifolds are provided for dialysis solution in which the flow path percolates through the bundle of fibers along exterior surfaces thereof, so that the two flow paths are separated by membrane surfaces defined by the capillary fibers, so that diffusion exchange can take place. Dialyzers of this type are sold by the Artificial Organs Division of Travenol Laboratories, Inc. under the trademark CF.RTM..
It is also known that microporous membrane material, in which the pores may be in the micron size range, are very desirable for use in the oxygenation of blood and also in membrane plasmapheresis. For example, the TMO.RTM. blood oxygenator sold by the Artificial Organs Division of Travenol Laboratories, Inc. utilizes a microporous polypropylene membrane. Also, other microporous hydrophobic membranes such as microporous polytetrafluoroethylene may be used for the oxygenation of blood. Likewise, certain known microporous membranes may be utilized for membrane plasmapheresis. Microporous membranes may be used for other diffusion operations, as well.
By the term "microporous" it is intended to mean that pores exist which permit air and other gases to rapidly pass through the walls of the tubing, while the membraneous walls of the tubing retain a semipermeable characteristic, i.e., restricting the flow either of a liquid passing through them as in blood oxygenators, or restricting a component of the liquid passing through them, such as blood cells in membrane plasmapheresis devices.
The designs of diffusion devices utilized by the commercial capillary tubing dialyzers would desirably be utilized with other types of diffusion devices. Particularly, it would be desirably used in conjunction with bundles of microporous capillary tubing for the oxygenation of blood, membrane plasmapheresis, or other diffusion operations in which microporous membranes are utilized. However, a significant manufacturing disadvantage has existed, rendering it very difficult to assemble bundles of microporous tubing into diffusion devices, where the ends of the capillary tubing are potted in a manner similar to the manufacturing techniques for capillary fiber dialyzers.
During conventional potting operations of capillary fiber diffusion devices, the bundle of fibers is inserted into its housing, and then the liquid potting compound impregnates the ends of the bundle, while the housing is spun about a central axis to hold the potting compound at the ends of the bundle. Conventionally, the amount of penetration of potting compound into the bores of capillary tubing at both ends thereof is substantially less than the level of potting compound permeating the bundle outside of the bores, because the air inside of the bores is compressed as the potting compound advances into the bores from both ends, causing a counterpressure which inhibits the advance of potting compound into the bores.
As the result of this, when the potting compound is cured, one can cut transversely through the middle of the potting compound at the ends of each bundle to expose open bores, which is necessary in order to obtain an operating diffusion device by this potting method.
However, in the case of microporous capillary tubing bundles, during the spinning step, as the potting compound advances into the bores of the microporous capillary tubing, there can be no increase of air pressure in the bores, because the air easily leaks out of the micropores of the capillary tubing. Thus, the level of the potting compound in the bores becomes essentially equal to the level of the potting compound outside of the bores in the bundle, with the result that it is difficult or impossible to form a potted bundle in which open bores pass through a cut section of potting compound to be open to the ends of the bundle.
In accordance with this invention, a method for effectively potting microporous tubing is provided, to permit such microporous tubing to be utilized in diffusion devices having, for example, the effective design of the current capillary fiber dialyzers, with the known manufacturing and functional advantages which are provided by that popular and effective design.
The invention of this application may also be used elsewhere, wherever it is desired to pot the ends of microporous tubing.